1. Field of the Invention
This invention generally relates to semiconductor packages, and in particular, to semiconductor packages having spacer strips that enable one or more semiconductor dies having central terminal pads thereon to be stacked on top of one another and reliably wire bonded to an associated substrate.
2. Description of the Related Art
A typical semiconductor package includes a connective substrate, such as a lead frame or a laminate, that has a semiconductor die, or xe2x80x9cmicrochip,xe2x80x9d mounted on a surface thereof and electrically connected to the substrate by, e.g., a plurality of fine conductive wires that bond at opposite ends to input/output terminal pads on the tops of the die and the substrate, respectively.
Some dies, such as memory chips, have their terminal pads located in a central portion of the die""s active surface, as opposed to at their peripheral edges. Wire bonding of these types of dies can be more problematical because the wires must traverse not only the vertical distance from the edges of the die to the substrate, but also a greater horizontal distance from the edges of the die to the centrally located terminal pads thereon. This increase in the distance traversed by the wires increases the possibility that one or more of the wires may contact the surface of the die and/or each other, and thereby short out. This problem is exacerbated if another die is stacked on top of the first die, as is sometimes done to increase package component density. The problem then becomes one of preventing the wires from shorting to the second die, as well as to the first die and each other.
A need therefore exists in the industry for a semiconductor package incorporating an apparatus that enables one or more semiconductor dies having central terminal pads thereon to be stacked on top of one another in the package and reliably wire bonded to an associated substrate without shorting of the bonding wires to the die(s) and/or each other.
This invention provides a semiconductor package incorporating xe2x80x9cspacer stripsxe2x80x9d that enable one or more semiconductor dies having central terminal pads to be stacked on top of one another within the package and reliably wire bonded to an associated substrate without shorting of the bonded wires.
The novel package includes a connective substrate having top and bottom surfaces. The bottom surface of a first semiconductor die is attached to the top surface of the substrate. The die has a top surface with a plurality of terminal pads formed on a central portion thereof.
A first pair of spacer strips is mounted on the top surface of the die at its opposite edges such that they straddle the central terminal pads on the die. Each of the spacer strips comprises a flat, elongated strip of an insulative material having a top surface, an opposite bottom surface that is attached to the top surface of the die, and a thickness between the top and bottom surfaces.
The die is electrically connected to the substrate by a plurality of fine conductive wires. In one embodiment, each of the wires has a first end bonded to a corresponding central terminal pad on the die, a second end bonded to a corresponding terminal pad on the first surface of the substrate, and an intermediate portion between the first and second ends that passes transversely across the first surface of a corresponding one of the spacer strips. The spacer strips have spaced transverse grooves in their top surfaces that captivate the intermediate portion of each individual wire, thereby redistributing the wires and isolating them from the die and from each other.
In another embodiment, the spacer strips have spaced bonding pads on their top surfaces. Each of the wires has a first end bonded to a corresponding central terminal pad on the die, a second end bonded to a corresponding terminal pad on the first surface of the substrate, and an intermediate portion between the first and second ends that is bonded to a corresponding one of the bonding pads on a corresponding one of the spacer strips.
In yet another embodiment, the conductive wires comprise associated pairs of wires. A first wire in each pair has a first end bonded to a corresponding terminal pad on the die and a second end bonded to a corresponding bonding pad on a corresponding spacer strip. A second wire in each pair has a first end bonded to a corresponding terminal pad on the substrate and a second end bonded to the same bonding pad on the spacer strip to which the second end of the first wire in the pair is bonded.
A second die can be mounted directly on top of the spacer strips on the first die. Alternatively, a second pair of spacer strips can be mounted on the bottom surface of the second die before it is mounted on top of the first die. Each of the strips in the second pair of spacer strips is positioned in facing opposition to a respective one the strips in the first pair of spacer strips on the first die. The strips cooperate to space the second die above the first die at a controlled distance and prevent the second die from contacting the bonding wires on the first die.
A better understanding of the above and other features and advantages of the present invention may be had from the detailed description below of certain exemplary embodiments thereof, particularly if such consideration is made in conjunction with the several views of the associated drawings.